[SRR]

One thing I didn't see mentioned here is the fact that from the factory clutch and flex fans had different size pulleys. The clutch fan uses a smaller size pulley on the water pump.

[Pontirag]

clutch fan is the way to go. The flex fans maybe work maybe not but at higher revs the tips reach the speed of sound and you start having problems. Like blade failure.

[Z Code 400]

I have conducted a number of experiments with the severe duty fan clutch and 18.5" 7 blade fan from a 454 Chevrolet Truck application Vs. the 18.5" 7 blade Lincoln Flex Fan. I used an AC Delco fan clutch and a Hayden fan clutch, both were of the 'severe duty' variety. (2) identical clutches were used during testing to ensure consistency between the two brands.

All tests were conducted on my 65,000 mile original 1975 Formula with 350 Pontiac engine and 160° Robertshaw thermostat.

With the clutch fan, the temperature would always run between 190° and 220° even when outside temperatures were below 50°F. I could allow the car to run at fast idle in the driveway for extended periods and the temperature would climb up to around 230° before the clutch would fully engage and bring the temperatures down to the 190° to 220° range again.

The temperature would run in the 190° to 220° range regardless of vehicle speed or load. In effect, the clutch fan regulated coolant temperature much like a thermostat.

The 7 blade clutch fan was also very noisy with audible 'buffeting' when fully engaged. Keep in mind, this is running the big (slow) water pump pulley that came stock on my non A/C Formula, which is much smaller than the water pump pulley used on the cars equipped with A/C, so I am definitely turning the fan much slower than normal on my application.

The 7 blade flex fan was pulled from a 1968 Lincoln Continental. It was installed with the factory 2.50" Pontiac spacer.

This fan is quieter at all engine speeds than the clutch fan, even when the clutch fan was only partially engaged. With the Lincoln fan, the coolant temperature stayed right on 160° regardless of outside temperature or vehicle load/speed. Even in 100°+ ambient temperatures, the car would not go over 175° even after prolonged periods of idling.

In my opinion, the added cooling benefit of the flex fan, in a mild street application, far outweighs any HP loss.

Hope this helps...Robert

[Region Warrior]

May just be the way you worded it.

A/C water pump pulleys are smaller(6-3/8") then non a/c's(8").

A/C crank pulleys are 8", and non a/c are 7-7/16".

I think alot of guys dont account for the difference in water pump speed.

Since my cars can rev over 6000, i use 19" flex rated to 10,000 rpm.

[sixt8bird]

Originally Posted by Z Code 400

I have conducted a number of experiments with the severe duty fan clutch and 18.5" 7 blade fan from a 454 Chevrolet Truck application Vs. the 18.5" 7 blade Lincoln Flex Fan. I used an AC Delco fan clutch and a Hayden fan clutch, both were of the 'severe duty' variety. (2) identical clutches were used during testing to ensure consistency between the two brands.

All tests were conducted on my 65,000 mile original 1975 Formula with 350 Pontiac engine and 160° Robertshaw thermostat.

With the clutch fan, the temperature would always run between 190° and 220° even when outside temperatures were below 50°F. I could allow the car to run at fast idle in the driveway for extended periods and the temperature would climb up to around 230° before the clutch would fully engage and bring the temperatures down to the 190° to 220° range again.

The temperature would run in the 190° to 220° range regardless of vehicle speed or load. In effect, the clutch fan regulated coolant temperature much like a thermostat.

The 7 blade clutch fan was also very noisy with audible 'buffeting' when fully engaged. Keep in mind, this is running the big (slow) water pump pulley that came stock on my non A/C Formula, which is much smaller than the water pump pulley used on the cars equipped with A/C, so I am definitely turning the fan much slower than normal on my application.

The 7 blade flex fan was pulled from a 1968 Lincoln Continental. It was installed with the factory 2.50" Pontiac spacer.

This fan is quieter at all engine speeds than the clutch fan, even when the clutch fan was only partially engaged. With the Lincoln fan, the coolant temperature stayed right on 160° regardless of outside temperature or vehicle load/speed. Even in 100°+ ambient temperatures, the car would not go over 175° even after prolonged periods of idling.

In my opinion, the added cooling benefit of the flex fan, in a mild street application, far outweighs any HP loss.

Hope this helps...Robert

Thats why I use the factory power flex fans on all my Firebirds. All run around 160-170 and never get hotter than that even in 100 deg traffic. Even my 12.5 sec non ported head 400 stays nice and cool in traffic.

[MikeNoun]

I've had the exact opposite results with my fan swaps over the years. The 18" clutch fan always kept my car at 180 degrees in any weather. An 18" flex fan, 7-blade stainless, allowed the temp to creep to 200. The same results were found when Hot Rod, Car Craft, PHR, and other magazines tested fans over the years.

All the Chrysler 426 Hemi's came with clutch fans, and so did nearly every GM car ordered with a trailering package, as well as nearly every GM car or truck built in the 70's and 80's. If GM used clutch fans for heavy-duty, high performance, or for trailering duties, you can bet the farm that they worked better than a fixed blade fan. GM wasn't stupid, and didn't invest millions of dollars in R&D, tooling, and adding extra cost into a vehicle, if a fixed blade fan would have worked better.

[PLAY400]

Flex fans work fine on stock vehicles. Once you start running a bit of gear, get the rpms over 2000 they start to flatten out and quit pulling air. Proved this many times on my 4x4. Need a solid blade.

[Region Warrior]

From memory. Need to write this stuff down.

With a 19" flex and 170 stat, waiting in line(650 rpm in drive), temp in 90* weather was 180-190.
By the time i let up in the box, it's 170-175.
While stagging, it slowly creeps back up to 180-185.
Before i can hit 2nd, its back down and stays down till i hit the return road.

It stays about 175 driving on the highway at 70 mph.

Anyone using clutch fans to 6500 rpm and higher?
Since i have a couple, may try one this year.
Also gon'a try a 180 stat.

[lust4speed]

Originally Posted by Z Code 400

...The temperature would run in the 190° to 220° range regardless of vehicle speed or load. In effect, the clutch fan regulated coolant temperature much like a thermostat...Robert

I've found that even new severe duty clutch fans can engage at a higher temperature than what the manufacturer claimed. For those of you that want to experiment, here's something to try:

The engagement of the severe duty fan is governed by the rotation of the center pin on the front of the clutch. This is the pin in the center of the bi-metal coil. As this pin is turned counter-clockwise, the fan engages. Due to manufacturing tolerances, this pin can be a little to far clockwise and won't engage until the temp is over 200°. Unhook the coil at its outside edge where it attachés to the body of the clutch and bend it from a 12:00 o'clock position to something like a 12:10 o'clock position. Don't get carried away or the fan will never freewheel (although a bend in the opposite direction will cure this). it doesn't take much of a movement to change the engagement temperature.

Bending the tang on the spring this way moves the coil just a little counter-clockwise which is the way you want to go. To prove this just take a heat gun before you start and apply a little heat to the coil and watch the center pin move counter-clockwise.

This will be correct for all fans that spin like the old Pontiac's - clockwise rotation. Some serpentine belts on newer engines change the rotation of the fan and this procedure has to be reversed for them.

As long as you don't get carried away and snap off the tang of the coil, this procedure is totally reversible.

[Z Code 400]

Originally Posted by MikeNoun

I've had the exact opposite results with my fan swaps over the years. The 18" clutch fan always kept my car at 180 degrees in any weather. An 18" flex fan, 7-blade stainless, allowed the temp to creep to 200. The same results were found when Hot Rod, Car Craft, PHR, and other magazines tested fans over the years.

Mike,

If you contact any source that documents Chrysler Hemi vehicles, you will find that all were equipped with the 6 blade, fixed pitch fan. I can attest to this as we have restored several to concours original. Chrysler did offer a flex fan as a dealer installed option.

The 429 Boss also used a flex fan, as did the 427 Fords in their highest-performance trim levels.

A very good friend of mine, Ben Arnold, who drove a Ford Taladega during the 1969 Daytona 500, told me that they were restricted by the rules to the factory, 4 blade, fixed pitch fan. However, he did conduct experiments with a clutch fan and they did not cool as well as a fixed unit. "They obviously made more horsepower, but they just couldn't cool the engine," he said in a recent conversation on this subject by phone.

Funny, don't you think? That Pontiac would put the #3998988 18.0" 7 Blade Flex Fan on a heavily optioned Safari wagon? Maybe you better call Pontiac and tell them a clutch would work better???

If you choose to conuslt the Pontiac Shop Manual, you will find the following written about the Power Flex Fan: "A five blade variable pitch fan is designed to reduce fan noise and improve airflow when maximun cooling is required. At high rpm, air flow through the grille is sufficient to maintain adequate cooling and the blades tend to straighten out, reducing the pitch angle by 50% at 5000 rpm. A five blade power flex fan is used on cars intended for severe service, such as police, taxi and trailer options."

I have proven the flex and fixed pitch fans superior for my cars, including those of customers. I use and recommend them. Your results may indeed vary...Robert

[MikeNoun]

Z Code 400, could you please explain why did GM made approximately 10 million of those expensive clutch fans, both thermal and non-thermal, all throughout the 60's, 70's, and 80's? Why didn't they use a cheap ol' 5-blade flex fan on ALL their cars and trucks? Maybe they should have contacted your friend that raced Talledega in 1969, and General Motors could have saved about $25 per car, or roughly $250 million dollars back then.

I believe your results, but as I said, many have had the opposite results. A clutch fan will save hp, but I don't quite understand how a fixed 18" 7-blade fan, with a clutch in the middle, using very wide paddles with curved tips to reduce noise, would pull LESS air at idle than a 18" 7-blade flex fan? All thing being equal, they would draw the same amount of air at idle, unless the clutch was bad, or the thermal setting was too high. Many of the GM thermal units were set to engage at 200 degrees during the 70's-80's emissions era, so hitting 210 degrees wouldn't be that unusual in an old Pontiac V8. Of course, we want 180-190 in our old Pontiacs, so perhaps the thermal unit you tested was the wrong temp.

Again, 2 fans, both 18", both 7-blade wide paddle models, one has a clutch, the other has flexible blades. How could the version with flexible blades pull MORE air than the version with fixed blades, unless the clutch wasn't fully engaged?

[Z Code 400]

Mike,

I cannot answer your question, I can only offer the results of my testing, what Ben Arnold experienced at Daytona in 1969 and the quotes directly from the Pontiac service manual.

However, I do have a theory....

There were many factors at play when the fan clutch was designed. If you study the old Ford and Chrysler service manuals, they state the fan clutch helped meet fuel economy standards. That is one possibility.

Additionally, if you study the Pontiac service manual, you will notice they describe the clutch as 'limiting fan rpm to 2200 maximum' under operating conditions. This would seem to be reflected in my testing as the fan definitely will unclutch hot at elevated rpms. According to several sources, a clutch fan never fully engages.

I have no way to substantiate this, but the 7 blade Lincoln fan definitely seems to pull more air, much more air in fact at all rpm's than the 7 blade GM fan with a severe duty clutch and it does so with much, much less noise and absolutley no 'buffeting' sound, common to both the 5 and 7 blade units I have tested with a clutch.

As you have correctly stated and supported by my testing, the clutch doesn't engage until at least 210°F, which isn't bad, but not what I want from my car.

Here is another question for you; Jim Hand, a well respected Pontiac guru reports power gains with a 'X-Pipe' that I have never seen duplicated here locally. In fact, one local shop has been pulling them off several cars recently when 0 HP and 0 lbs/ft of TQ were realized during actual dyno testing. I believe Jim Hand's results, but I also believe what I have seen here locally.

My point is, you should test the clutch and the flex fan and then use what works for you.

That's the best advice I can give you...Robert

[MikeNoun]

Robert, I've had several fans on my cars over the years, and like most classic Pontiacs, I always ran hot (65 GTO-389 & 400, 79 Trans Am-403 & 400, 69 Firebird-400 & 455). When someone gave me the advice of running a clutch fan, I laughed, but I tried it, and I've never looked back. Then I read a detailed write-up in a magazine that tested several different fans, and the clutch fan won, much to the chegrin of the magazines advertisers that all sold flex fans.

Air conditioned cars need superior cooling systems. The 1969 Pontiac Service Manual shows a thermoclutch fan as standard equipment on ALL air conditioned cars (except the 428 HO), and the thermal clutch fan was optional on all other Pontiacs. I'm not sure why Pontiac would spend the time tooling up special deflector baffles to force more air into the radiator, equip an a/c car with a larger radiatior (and other items) to help the car run cooler, then stick a fan up front that was VERY expensive to produce when they could have just used a cheap ol' flex fan on every model and called it a day.

It may or may not be true, but someone a long time ago made a comment that the reason the clutch fans were not used on some of the ultra high hp cars of the 60's was because of steep gears, radical camshafts, and warranty issues. The clutch fans were being tortured because of erratic idles caused by aggressive cam profiles, and there were warranty issues with Musclecars cruising at 3500-4000 rpm, with 3.73 or steeper gears, for hours at a time on the highway.

I was incorrect about the thermal clutch fan being used on the Hemi. The thermal clutch fan was used on all the high perf and non-high perf Mopars that were equipped with a/c, from the Cudas to the Challengers, from the 318 up to the 440, but not the Hemi.

[Z Code 400]

Mike,

I have often wondered if the higher pulley speed of an A/C equipped car, coupled with concerns for fuel economy, was one of the reasons a clutch was employed on those applications? According to several GM service manuals, the fan clutch actually governs fan rpm to about 2200 rpm. Since the clutch never fully engages, this built in 'slippage' could be a way of improving fuel economy with the very high pitch angles of the blades used with a fan clutch.

I have seen some cars that used the old fan clutch eliminator and when running full pulley speed, they almost always caused the belts to squeal.

Your theory on warranty concerns also makes good sense...Robert

[Region Warrior]

Dailey street cars are alot different then street/strip cars.
Theres alot things.
Radiator size.
Air flow to radiator.
Fan shroud/no fan shroud.
Blades located correctly into shroud.
Pulley size.
What works for one probly wont for another if thier set up is different.
Probly said it earlier, but have used both depending on application for 30 plus years with out problems.

I say Pontiac used the fan they did on 69 RAIV's for the same reason you couldnt get A/C.

[Bob Arthur]

Old fan clutch eliminator? I did a search with no results but this sounds like a good trouble shooting tool. I have an idea how this works but is there something available or is it self-made?

[lust4speed]

The fan clutch eliminator was nothing more than a spacer that would physically eliminate the fan clutch. This was one of those 1970's ideas that appealed to people that were too cheap to put the money out for a correct replacement fan clutch. Not a good idea because it locks the stock fan to the pulley speed - bad because it isn't safe to run the heavy stock fan over about 4,400 RPM, and bad on gas mileage and noise because the fan is running 100% all the time.

All the flex fans are rated up to 10,000 RPM and the spacer (not fan clutch eliminator) simply adds the needed distance to put the fan in the proper location. Use the fan clutch or the flex fan, but don't use a fixed stock fan.

[Z Code 400]

Originally Posted by Bob Arthur

Old fan clutch eliminator? I did a search with no results but this sounds like a good trouble shooting tool. I have an idea how this works but is there something available or is it self-made?

Bob,

They are still available from Jeg's and Sumit. They replace the clutch and allow the fan to run at full pulley speed. They recommend it not be used on any application where engine rpm is above 4200 if I recall correctly.

Dad used one for years on an old 6.2 Litre Diesel. One morning, it developed a severe vibration and he found the fan had spit 2 blades off. Those big, aggressive blades, used with a fan clutch, were never designed to run at full pulley speed. In fact, according to several GM service manuals, a clutch governs fan speed to roughly 2200 rpm. They (fan clutches) never allow the fan to run at full pulley speed when they are working correctly.

One of the best fans out there for high performance work is the 18.0" 7 blade, fixed-pitch fan that was found on the 426 Hemi and Non-A/C versions of the 383 and 440 MoPars. It is a common find in the junk yards, as it was used on many Slant-Six applications. It is easily identified by part number 2863213.

It is durable, very quiet, even at elevated rpm's and pulls a tremendous amount of airflow. I have included a photo for reference...Robert

[Z Code 400]

Another thing I have noticed when swapping the solid and/or flex fans onto factory fan clutch applications is the additional cooling benefit, even on vehicles that don't have a cooling problem.

We have a 1985 Suburban that has been in the family since new. It always cooled well with the factory 19.0" 5-blade fan and HD thermal clutch. The factory thermostat was a 195° and we replaced it years ago with a 180° variant, but the vehicle still ran at 200° to 220° under all conditions, identical to the way it ran with a 195°F thermostat installed.

After I recently overhauled the original 350 engine, I installed a 160° thermostat and a brand new AC-Delco Fan Clutch, specific to that application. As usual, the Sub ran 200° to 220° under all conditions, even when outside temperatures (at night) were only 39°F.

Just as an experiment, I installed the 7 blade 18.0" Lincoln fan and 2.5" spacer that I had been using on my 1975 Formula. With no other changes, the coolant temperature would not go above the 160° thermostat opening point. My fiance began complaining that the heater wasn't getting hot, so I installed a 190° unit and the coolant temperatures would not go over 200°F under any conditions.

When I put the clutch fan back on, temps went right back to 220°F. When I installed the old fan clutch, there was no change and you could hear both clutches modulating on and off as the engine was running.

This is also representative of the testing I have conducted on other people's cars. In my personal experience, it would seem that the clutch fan regulates overall coolant temperature, much like a thermostat.

Just an observation...Robert

[pontiac 455ho]

i run the flex fan 313. runs 185 all day